There is growing interest in the use of bioethanol to supplement fossil fuels as an energy source in transport. For example, ethanol accounted for 9% of gasoline consumption in the USA in 2009, and 90% of the ethanol produced in the USA in 2009 was produced using corn as feedstock. The majority of existing corn ethanol mills, and almost exclusively all the corn ethanol mills commissioned in recent years, are so called “dry mills”.
A “dry mill” plant processes corn into ethanol through a dry grinding process. The ground corn is mixed with water to form mash, and then an enzyme is added to convert corn starch into sugar. A fermentation process is followed to convert the sugar into ethanol. The liquid intermediate, called “beer,” is further processed by distillation and ethanol is collected. The leftover in the “beer” after the removal of ethanol is called stillage, which contains water, protein, nutrients, fibre, and corn oil. The stillage includes an aqueous phase and an oil phase. The corn oil may be separated from the stillage by using a centrifuge and collected as a higher value co-product. A separation additive may be added into the stillage to enhance the separation of the oil phase from the water phase and increase the corn oil yield. Ethanol plants may treat whole stillage from the “beer” column via centrifugation to produce wet cake and thin stillage, and further treat the thin stillage stream by subjecting it to multiple effect evaporation to increase the solids content and recover the distillate for return use in the process. As the solids content increases, the thin stillage is typically referred to as syrup. The syrup is typically combined with wet cake or distillers' dry grains (DDG) and sold as animal feed.
The corn oil yield from a stillage depends on many factors, such as corn kernel quality, water content, the particle size of the solids in the stillage, the process temperature of the stillage in the centrifuge, and the design of the separation equipment. The use of a corn oil separation additive is intended to increase the corn oil yield.
WO2012/128858 of Hercules Incorporated discloses the use of polyoxyethylene(20) sorbitan mono-laurate (polysorbate 20), polyoxyethylene(20)sorbitan mono-stearate (polysorbate 60) and polyoxyethylene(20)sorbitan mono-oleate (polysorbate 80) as corn oil separation additives. The specific additives disclosed in WO2012/128858 are all based on sorbitan and although the yield of corn oil obtained from stillage in the presence of such additives is improved, there can still be a significant amount of corn oil left un-collected, and discharged unseparated from the stillage as part of a product with lower commercial value. The composition of the stillage can vary considerably as can the effectiveness of the sorbitan derivatives as oil separation aids with different stillages. There is a need for alternative or improved separation additives which are also effective with a wide range of stillages.
The present invention seeks to aid the recovery of oil from a wide range of aqueous compositions, particularly from different biomass materials, and especially from different stillages.